Many industrial processes use active materials that need to be supported on shaped bodies or that need to be bound in shaped bodies, so they can be handled and loaded in reactors. Examples of such catalysts include supported metals, supported metal complexes, supported organometallics, bound zeolites and bound zeolite-type materials. Shaped bodies are typically made of silica, alumina, alumino-silicates and other types of inorganic refractory oxides. Inorganic oxide catalyst shaped bodies are typically prepared by forming a mixture of one or several sources of the inorganic oxide in a suitable vehicle, said vehicle typically being water, an organic solvent or mixtures thereof. The mixture is formed into particles of various shapes, dried and calcined.
In order to be used as catalyst carriers, these bodies must have appropriate surface properties, sizes, shapes and porosities to carry the desired amounts of active materials and to enable catalyst handling, especially during reactor loading and unloading. The shaped bodies must also be strong enough to sustain catalytic conditions, and they must also have appropriate porosities and shapes to avoid high pressure drops across the reactor and allow the desired catalytic reactions to take place.
The choice of catalyst carriers will depend on various factors, such as, for example, the type of catalytic material used, the required catalyst strength and the required diffusivity across catalyst particles.
While silica shaped bodies have been known for a long time and are commercially available in various forms, silica shaped bodies having large pores are not easy to obtain on large commercial scale, for technical and economic reasons. One of the technical problems in forming particulate inorganic material, such as silica, resides in the difficulty in forming suitable plasticized mixtures that can be processed in conventional particle forming equipment, such as extruders, for example.
U.S. Pat. Nos. 6,576,120 and 6,709,570 disclose a method for preparing catalysts comprising ZSM-5 and silica which comprises: (a) preparing an extrudable mass by first mixing ZSM-5, an amorphous precipitated silica and an acid colloidal silica into a first homogeneous mixture having a pH below 7 and subsequently adding ammonia to the first homogeneous mixture such that the pH of the resulting second mixture has a value of above 8, (b) extruding the extrudable mass resulting from step (a), (c) drying the extrudate resulting from step (b); and, (d) calcining the dried extrudate resulting from step (c).
International Publication Number WO 2006/026067-A1 describes a method for the manufacture of a structured body, which process comprises (a) preparing a batch composition free of organic solvent comprising (i) at least one particulate inorganic material, (ii) at least one particulate silicone resin of average particle size 700 microns or less, and (iii) water, and (b) forming the batch composition into a structured body. While this method provides shaped bodies with excellent properties, it requires the use of silicone resins that can be expensive if used on a very large scale.
We have now found a new method for making silica shaped bodies that uses plasticized mixtures that can easily be prepared and processed in large commercial scale particle forming equipment. Furthermore, the method of the invention allows to make silica shaped bodies of varying pore sizes, to meet the needs of a wide range of uses for the shaped bodies made by such process.